This invention mainly relates to a receiving housing for a reaction disk and to a pneumatic servomotor for an assisted braking, including such housing fitted with its reaction disk.
It is quite usual to amplify the force, which a driver exerts on a brake pedal, by means of a pneumatic servomotor (also called a xe2x80x9cboosterxe2x80x9d), comprising a variable-volume front chamber, separated from a variable-volume rear chamber by a tight flexible diaphragm and by a rigid skirt driving a pneumatic piston which bears, through a push rod, on the primary piston of a tandem master cylinder of a hydraulic braking system. The front chamber, directed towards the tandem master cylinder, is hydraulically connected to a vacuum source whereas the rear chamber, in the opposite direction to the front chamber, is hydraulically connected, using a valve control, to a propellant fluid source, typically atmospheric-pressure air.
At rest, that is when the driver does not actuate the brake pedal, the front and rear chambers are interconnected, while the rear chamber is isolated from the atmospheric pressure. On braking, first the front chamber is isolated from the rear chamber and then air is admitted into the rear chamber.
Unfortunately, when the brake pedal is depressed, the sudden opening of the air-supply port of the rear chamber causes the pneumatic piston to move forward too fast. The initial resistance to the travel of this pneumatic piston is quite weak. As a matter of fact, on the one hand, there is a great pressure difference between the front and the rear chambers of the servomotor and, on the other hand, the operational clearances of the tandem master cylinder are taken up. This swift advance of the pneumatic piston may cyclically open the passage connecting up the front chamber and the rear chamber, which generates a noise resembling that of wipers set in motion on a dry windscreen and therefore called a xe2x80x9cwiper noisexe2x80x9d in the art. Such noise, although normal, is considered quite unpleasant by the users who fear some dysfunctioning of the system. Besides, the reopening of the passage connecting up the front and rear chambers of the servomotor reduces the assistance efficiency at the beginning of the braking process.
Therefore, it is an object of the present invention to provide a servomotor for an assisted braking, ensuring a noiseless running, especially by a reduction of the so-called xe2x80x9cwiper noisexe2x80x9d to the minimum.
Another object of this invention consists in providing a servomotor for an assisted braking with a quite high efficiency.
It is also an object of the present invention to provide a servomotor for an assisted braking, ensuring a quick-acting assistance.
It is another object of this invention to provide a braking system including a pneumatic assistance servomotor and a tandem master cylinder, equipped with superassistance means for emergency braking situations, of the types described in EP 0 662 894 and FR 2 751 602, and having a low variation of the starting threshold of superassistance means in the case of an emergency braking situation.
These objects are achieved, in accordance with this invention, by a pneumatic servomotor for an assisted braking, fitted with means capable of resisting too fast a forward travel of the pneumatic piston when the brake is actuated, which otherwise might lead to an undesired reopening of the passage connecting the front chamber with the rear chamber of the assistance servomotor.
These objects are achieved according to this invention, in that the compliance of a reaction disk is turned into account so as to resist too fast a forward travel of the piston. In the preferred embodiment of the invention, the substantially incompressible reaction disk is accommodated inside a housing, the inner space of which is greater than the volume of the disk. The deformation of the disk, during an initial braking stage, will result in a such a deformation of the disk as to enable it to fill completely its housing, which makes it act conventionally in the course of a subsequent braking stage. The applying of the reaction disk onto the distributor plunger or onto any other part, interlocking with the control rod for the control of the flaps, limits the forward speed of the pneumatic piston, when the brake is actuated, and prevents or restricts the undesired reopenings of the connecting passage between the front and rear chambers of the assistance servomotor.
The main subject of this invention is a receiving housing for a reaction disk, said housing being defined by stationary walls and by moving walls and accommodating an incompressible reaction disk of a braking servomotor, said reaction disk comprising a contact area associated with an element driven by a brake pedal, characterised in that, when the contact is made between the reaction disk and the element driven by the brake pedal, the housing of the reaction disk has an area which is taken by the incompressible reaction disk, and an area filled with a compressible fluid, enabling, in a first braking stage (jump stage) of the braking process, an elastic deformation of the reaction disk so that the latter may resiliently exert a mechanical reaction on said element driven by the brake pedal, and in that, during s second braking stage (the actual braking operation), the incompressible reaction disk will fill its housing in a substantially complete manner.
The present invention also deals with a housing, characterised in that it comprises two adjacent coaxial cylindrical areas, the first area having a first diameter corresponding to that of the reaction disk, and the second area having a second diameter, which is smaller than the first diameter.
Another subject matter still of the present invention is a housing, characterised in that the second area is radially bounded by a washer.
According to another aspect of the invention, a servomotor for an assisted braking is characterised in that it includes a housing.
The present invention also deals with a servomotor, characterised in that the housing is fitted with a reaction disk, including a radially-outer annular area which defines, together with the walls of the housing, an area of said housing to be filled with a compressible fluid.
Another subject matter still of the present invention is a servomotor, characterised in that the element driven by the brake pedal is a distributor plunger and in that the latter comprises a stub to be applied onto the reaction disk.
According to another aspect of the invention, a servomotor is characterised in that the reaction disk comprises at least one passage for the supply and discharge of the compressible fluid, respectively into and from the compressible area of the housing for the reaction disk.
Another subject of the invention is a servomotor, characterised in that, at rest, the element, which is driven by the brake pedal, is in contact with the reaction disk.
This invention also deals with a servomotor, characterised in that the element driven by the brake pedal comes into contact with the reaction disk, just as the flap closes for the tight separation of the front and rear chambers of the servomotor.
Another subject matter still of the present invention is a servomotor, characterised in that the reaction disk includes a resilient reinforcing insert.
Other features and advantages of the present invention will be apparent from the following detailed description, by way of example and by no means as a limitation, when taken in conjunction with the accompanying drawings.